A knee goniometer device is a bio-medical measuring device used in the rehabilitation setting to measure an anatomic angle of the knee. The knee goniometer may be used by orthopedic surgeons, physician assistants, and especially clinicians such as physical therapists, athletic trainers, and physical therapy assistants, etc. The knee goniometer device is used by a practitioner to measure the lack of knee extension, commonly known as straightness. In some instances, it may be used to assess hyperextension, also known as excessive straightness. Also, it may assess knee extensor length, often referred to as “quadriceps flexibility”.
Knee extension, hyperextension, and knee extensor length may become a problem with arthritis, injury, or after surgery. Patients who have experienced major knee trauma, with or without a later surgery, may have motion loss or hypermobility. A lack of extension may be called a “knee flexion contracture” because the knee motion is restricted in a small amount of flexion (bend). The average knee range of motion is 0 to about 135 degrees; some research reports 140 degrees. Often, a person may have an amount of hyperextension (straightness beyond zero) because of a person's anatomy structure or by injury. Hyperextension is sometimes noted in medical charts as a positive. For example, the person would have +5 to 135 degrees range of motion. On a standard “disc” goniometer (indicia are in degrees), 0 degrees indicates full (normal) extension, whereas 5 degrees hyperextension is within normal limits. Knee extensor length indicates a person's quadriceps muscle tightness.
A standard “disc” goniometer provides an angle reference measurement read by a user while the “disc” goniometer is held alongside a patient's knee. The “disc” goniometer requires a user to align one reference arm with the patient's upper leg, and a second reference arm with the patient's lower leg. The precision of the angle measurement relies on user expertise and perspective because the “disc” goniometer does not positively engage any part of a patient's leg. Measurements may vary based on a change of user or change in “disc” goniometer model type.
After surgery, it is important to regain normal motion as soon as possible in most protocol cases. Although, in a posterior cruciate ligament (PCL) reconstruction, rehabilitation is different as hyperextension is not desired. Ideally, restoring full knee extension properly allows for normal walking, improved function, and less pain. During post-surgical physical therapy, doctors commonly emphasize to patients that extension needs to be worked on more than flexion, because the connective tissue properties of the knee allows flexion to advance easier. Usually the goal is to attain the same amount of extension and knee extensor length in the surgically repaired knee as non-injured knee.
Documenting the amount of extension or knee extensor length helps with insurance coverage, indication of progress, and patient motivation. The knee goniometer may also be used for orthopedic research.